IRIS+ intermittant GPS and Compass errors

I’m having a frustrating collection of errors here that are difficult to reproduce on any given flight, and I’ve reached the limit of my troubleshooting. I’m getting GPS and Compass errors that pop up mid-flight, or sometimes don’t. The errors point to hardware malfunction, but maybe I’m missing something simple. At this point I can’t safely fly it in Auto mode, as these errors will suddenly pop up in the middle of a mission (see log from today).

I’m on 3.2.1 and have carried out multiple compass and accel calibrations since upgrading. The external GPS is doing great with fast locks and extremely low HDOP, and I have two of them now, so I’m very suspicious about the GPS error reports.

I have an external 3DR Ublox GPS+Compass installed by the book on a mast as the primary, with the internal compass set as secondary via serial 4/5 port. Seems fine some of the time. Problems started popping up soon after I installed it, but they seem to come and go. I suspect the compass in this unit is bad, but I’m also getting the GPS errors and occasional IMU errors…just kind of a mess.

Two logs attached, 2015-05-28 has IMU logging, the other is a log from an aborted mission this AM without IMU logging.

Does this look like hardware malfunction to you? Thank you, I’m out of options here other than ditching the external GPS/compass altogether, which would be a shame since the GPS performance is great.
[attachment=0]2015-06-10 10-14-48.log[/attachment]
The log with IMU is too large, it can be downloaded here … sp=sharing

I should add that I’ve operated with and without the internal GPS as a secondary connected to serial 4/5 without detectable improvement of the errors, so I’ve ruled out a primary/secondary GPS conflict. I understand that the internal compass is not used with the external Ublox installed, so I guess I’m ruling out a primary/secondary compass conflict as well. I’ve also had trouble getting a successful accel calibration, but eventually pulled it off and it’s flying really well in Stabilize…until it starts making the EKF/Internal Nav Failure sound and gets squirrelly.

Arrgh, the line above “with the internal compass set as secondary via serial 4/5 port” should read “with the internal GPS set as secondary via serial 4/5 port”.